Diving equipment has undergone rapid development enabling divers to descend to ever increasing depths. As the capability to do so grows, so does the demand for means to ensure the safety of the divers to the maximum extent.
One area of particular concern is the sealing of the face masks to the face. While the sealing of the masks is an obvious requirement, problems in the way of meeting that requirement are that facial features vary greatly while the seal must be subjected to adequate sealing pressure all the way about the mask cavity which accommodates the nose and overlies the mouth and the cavity must usually be of minimum volume to minimize its contribution to respiratory dead space. Where the gas within the helmet may contain a dangerous percentage of carbon dioxide, the effectiveness of the mask seal is particularly important.